Lyme disease is a debilitating condition that has become a significant public health concern. The disease is caused by infection with a pathogenic Borrelia bacterium (a spirochete) and is transmitted by the bite of various species of Borrelia-infected Ixodes ticks. Accurate and early detection of Lyme disease is critical to effective treatment. The only clinical symptom sufficient for diagnosis of Lyme disease is the presence of erythema migrans, a rash having a distinctive bulls-eye appearance. However, erythema migrans is only present early during infection and, even then, does not appear in all infected individuals. Other clinical symptoms that have been associated with Lyme disease, such as Bell's palsy, are not specific enough, either alone or in combination, to determine clinical diagnosis in the absence of erythema migrans.
In the absence of erythema migrans, the basis for diagnosis of Lyme disease is an antibody response to a pathogenic Borrelia species, such as Borrelia burgdorferi, Borrelia afzelli, or Borrelia garinii. In North America, the Center for Disease Control (CDC) recommends a two-tier approach tier serodiagnosis of Lyme disease consisting of a sensitive first-tier assay, such as ELISA, followed by a western blot if the first tier assay is positive or equivocal. First tier assays have traditionally made use of a whole-cell Borrelia burgdorferi antigen or recombinant Borrelia proteins. Such assays can be difficult to interpret, though, and are complicated by Borrelia antibodies arising from vaccination rather than infection. In addition, whole cell sonicates used in some Borrelia assays react with Treponema antibodies.
More recently, the C6 peptide assay, based on the conserved IR6 domain of the variable surface antigen (VlsE) of Borrelia, has become widely accepted as a first-tier assay having a high degree of sensitivity for disseminated and late Lyme disease. The C6 peptide assay uses a single 25 amino acid sequence of the Borrelia burgdorferi VlsE protein as the test antigen. Although it has been suggested that the C6 peptide assay may be suitable for a single-tier approach to diagnosis of Lyme disease, it is becoming apparent that the C6 assay is not sufficiently sensitive for such purposes because it fails to detect certain strains of infectious Borrelia. 
Accordingly, there remains a need in the art for additional assays for detecting Borrelia antigens and serodiagnosis of Lyme disease.